Plastic footwear and methods for fabrication



Feb. 11, 1969 J H ET AL 3,426,454

I PLASTIC FOOTWEAR AND METHODS FOR FABRICATION Filed April 24, 1967 'S heet of-3 INVENTORS James G. M/fc/zefl BY W/na/ee 6. M/fchefl @kfQ jluigg Feb. 11, 1969 J MITCHELL ET AL 3,426,454

PLASTIC FOOTWEAR AND METHODS FOR FABRICATION Filed April 24, 1967 Sheet 2 of :3

FIG.6 -7

Feb. 11, 1969 J, G, M|TCHELL ET AL 3,426,454

PLASTIC FOOTWEAR AND METHODS FOR FABRICATION Filed April 24, 1967 Sheet 3 of Fig. /2.

United States Patent 3,426,454 PLASTIC FOOTWEAR AND METHODS FOR FABRICATION James G. Mitchell and Winalee G. Mitchell, both Principle Business Enterprises, 205 Farnsworth Road, Waterville, Ohio 43566 Continuation-impart of application Ser. No. 451,181, Apr. 27, 1965. This application Apr. 24, 1967, Ser. No. 634,426 U.S. Cl. 36-25 Int. Cl. A43b 3/00, 11/00 9 Claims ABSTRACT OF THE DISCLOSURE Related application This application is a continuation-in-part of our prior copending application Ser. No. 451,181, filed Apr. 27, 1965, now abandoned.

Background ofthe invention There appears to be only limited availability of disposable footwear at present, despite the many advantages which can be realized from the use of such footwear. This is indeed unfortunate, since persons often find themselves in situations in which conventional foot apparel offers something less than ideal comfort or utility.

Some early attempts were made at fabricating crude foot-coverings of paper for use in public places where people commonly go barefoot, such as in the locker-room areas of public swimming pools, for example. These attempts, however, met with little success, due to the wellknown effects of water on paper. The advent of stretchy synthetic polymeric material in cellular and non-cellular sheets made available a water-resistant substitute for paper. In view of the availability of such materials and the demonstrable benefits to be obtained through the utilization of strong sanitary disposable foot-Wear, it may seem surprising that such footwear has not become a staple article of commerce.

One explanation for this rather surprising state of affairs is that there is an apparent paucity of knowledge as to how these new materials should be employed to best advantage in the manufacture of slippers. Specifically, we have found that previously known forms of slippers are, when fabricated of the new stretchy synthetic polymeric sheet material, so expensive as to deter their use as disposable slippers. Also, we have found that previous ideas on how to form slippers of synthetic polymer sheeting, especially cellular or foam sheets, are deficient in that the strengths of the material are not used to full advantage while the Weaknesses thereof are emphasized. Thus, very careful handling of the slippers is required if premature tearing or splitting of the material is to be avoided. This is particularly a problem with a slipper which has a forwardly inclined generally vertical seam at the back, which slipper stretches over the wearers heel when donned. Such seams have in the past displayed a tendency to part where they meet the upper edges of the sides of the slipper and may then fail completely, tearing from one end to another. Clearly, there is an existing need for strong, sanitary and inexpensive footwear and for eflicient methods of making such footwear.

Objects It is a princapal object of this invention to fill this need. It is a further object of this invention to provide novel items of footwear. Another object is to provide footwear of stretchy synthetic polymeric sheet material having novel arrangements of parts which render them readily adaptable to rapid mass-production methods. Still another object is the provision of methods, including unusual and new combinations of process steps particularly useful for the fabrication of slippers. Another object is to provide slippers and methods of making them of stretchy, cellular synthetic polymer sheeting material in and as a result of which a heel portion of improved strength is provided. Other objects and advantages of the invention will be apparent to those skilled in the art upon consideration of the following description of the invention and certain preferred embodiments thereof.

Brie summary of the invention In accordance with the invention, we have provided two novel forms of slippers and improvements in heel structures which are applicable to these two novel forms of slippers and to other slippers. The two novel slippers disclosed herein and those other slippers to which our improvements in heel structure are applicable are characterized by certain common features, including side portions of stretchy synthetic polymeric sheeting material and a generally upright but forwardly inclined seam at the rear of the slippers. The side portions meet and are secured to one another along this scam, e.g. as by heat sealing. The seam extends an appreciable distance ver. tically along the heel and may or may not terminate near the base of the heel. The upper end of the seam, however, intersects with the upper edges of the side portions, and it is at this point of intersection where tearing of the heels of prior art slippers has tended to begin at this point of intersection and to proceed down this scam along the heel. The improvement in heel structure provided by the present invention involves forming the heel so that the forwardly inclined heel seam and the portions of the upper edges of the side portions which are adjacent the seam meet at an acute angle. The acute angle provides an excess of stretchy material at the aforesaid point of intersection which, as the heel is stretched, is deflected downward, providing a zone or area of reduced tension in the material around the seam where it meets the upper edges of the sides. The excess material which is thus provided may be very small in quantity, but has a pronounced effect on heel strength. The angle need not be particularly acute and may closely approach a right angle where there is curvature in both the seam and the edges of the side portions where they meet. When the slipper is in wearing position, the acute angle may not even be visible due to the stretching and deflection of the material. Thus, the acute angle is best viewed while the slipper is not being worn and while the sides are flat tened against one another. Despite the fact that this change or improvement in heel structure seems quite small, it produces an unobvious and valuable improvement in the strength of the slipper.

Description of the drawings The invention may be better understood when the description of certain preferred embodiments appearing hereinafter is considered in connection with the accompanying drawings, in which:

FIGURE 1 is a perspective view of a first novel slip per corresponding with the invention;

FIGURE 2 is a top plan view thereof;

FIGURE 3 is a front view thereof;

FIGURE 4 is a side elevation thereof;

FIGURE 5 is a sectional view of apparatus for performing the method of the present invention.

FIGURE 6 is a plan view of a portion of FIGURE 5;

FIGURE 7 is a plan view of a portion of FIGURE 5;

FIGURE 8 is a sectional view of a portion of FIG- URE 5 FIGURE 9 is a broken-out sectional view taken along section line 99 in FIGURE 6;

FIGURE 10 is a side elevation of a second novel slip- P FIGURE 11 is a front view thereof; and

FIGURE 12 is a rear view thereof.

Description of preferred embodiments In accordance with the invention, we have provided a first novel slipper which includes a first piece of elastic, heat-scalable synthetic polymer foam sheeting of elongated shape. The piece of foam has two elongated sides and two ends. The first piece of foam material is connected to a second piece of like material of substantially similar size and shape along the first elongated side and along both ends of each. The pieces of material are also bonded along a portion of their second elongated sides.

The connected portions extend from about /5 to about /2 the length of the slipper along said second elongated sides from their first ends towards their second ends. The remaining portions or about /5 to about /2 of the above-mentioned second sides, are substantially free of attachment to one another.

The means of connection or attachment between the pieces of material may be crushed fused portions defining a seam or heat seal. The portions of the second sides of said pieces, which are substantially free of attachment, define a foot-opening.

When the slipper is in an unstretched condition with both pieces of foam material flattened, the edges of the unattached portions of the second sides meet the abovementioned seam or seal at an acute or right angle. This angular relationship is responsible for the durability of the slippers of the present invention. This relationship is preferably employed at both ends of the foot-opening, but it would not be a departure from the invention to use it at one end only, especially at the end nearest the heel of the slipper where the danger of tearing the seam appears greatest.

A modification falling within the scope of the invention is to form the slipper from a single piece of foam material which has been folded over upon itself to form two thicknesses in face-to-face relationship, which may then be united to one another as though they were two separate pieces. Thus, the terms first piece and second piece of foam employed in this specification and in the appended claims should be understood to refer not only 4 to pieces of foam which were originally wholly separate, but also to pieces which were originally part of the same sheet or strip of foam material.

In accordance with a method of the present invention, a first and a second strip of elastic, heat-sealable synthetic polymer foam are brought together in face to face relationship. The strips are then compressed in a narrow first region partially enclosing an elongated area having elongated sides and ends. The length and width of the enclosed area are slightly smaller than the width and length of the size foot for which the slipper is being made. This region of compression extends continously along the second end of the area, along the first elongated side, along the first end and about /5 to about /2 of the way along the second elongated side towards the second end. Suflicient heat and compressional force are applied to the aforesaid compressed region to rapidly develop a heat seal, e.g., in less than about 1 second. Along the remaining portion of about to about /2 of their second elongated sides, the strips are simultaneously compressed in a second narrow region in which the extent of compression is from about 20 to about 30 thousandths of an inch less than in the first region, so that substantially no permanent sealing of the strips to one another can occur in said second region. The ends of the first narrow region connect with the ends of the second narrow region. At each point of connection, the outer boundaries of the connected regions define a right or acute angle. While the strips are still under compression, the material within the above-described regions and the area of said strips enclosed by said regions is separated from the remainder of the strips.

In accordance with a particularly desirable embodiment of the invention, as shown in FIGURES 1 through 4, a slipper 1 is formed of elastic polyurethane foam sheeting in accordance with the foregoing method of the invention. We prefer polyurethane foam, but other bondable foam sheeting containing different polymeric materials, e.g. vinyl, may be used. The preferred slipper is made of 2 pieces 2 and 3 of the foam material. Each piece has a first elongated side 4 which is preferably straight or substantially so along at least about half of its length in order to provide a good fit. The ends 5 and 6 of each piece of foam material may be curved as shown, or may have any desired shape. For instance, the end 5 may be tapered or pointed to provide a slipper with a pointed toe. The pieces 2 and 3 are bonded at their edges in a narrow crushed and fused region 9 constituting a seam which extends continuously around curved end 6, elongated side 4, curved end 5 and partway along second elongated side 7 from end 5 towards end 6. The seam extends a distance d along side 7 which constitutes about A of the length l of the slipper. Along the remaining portion 8 of the second side of each of the pieces 2 and 3, the pieces are substantially free of any permanent attachment to one another. The unattached portions define the edges of an elongated foot-opening. The edges of this foot-opening may be straight, as shown, or may have any desired shape for decorative effect, such as wavy, saw-tooth and so forth. However, whether these edges are straight or some other shape, they must intersect with the ends of the seam 9 at a right or acute angle, the latter being preferred, such as acute angles A and B shown in FIGURE 4. This angular relationship has been found to spread tearing forces away from the ends 11 and 12 of the seam 9, thus discouraging any tendency for the seam to tear apart as the slipper is handled or worn.

A particularly preferred embodiment of the method of our invention will now be described in connection with apparatus which has been found suitable therefor. As disclosed in FIGURES 5 through 9, two strips of foam sheeting 40 and 48 are brought into face to face relationship. The strips may unwind from supply rolls 38 and 47 and may be fed by pairs of rolls 58-59 and 6061,

driven in synchronization by any suitable motor means 83. The motor means is adapted to feed the strips incrementally through a cutting and sealing station 49 shown in FIGURES 5 and 8. At cutting and seal ing station 49 there is a stationary lower sealing die 67 having an upwardly disposed horizontal die face 51, as shown in FIGURE 6. Sealing die 67 has a second upwardly disposed horizontal die face 64 which is somewhat relieved or lower than die face 51, as shown in FIGURE 9. The amount of relief R may be varied, but generally speaking, we have found that R should be about 0.010 to about 0.015" for best results. It should be noted also that in the disclosed dies, the die faces 50 and 51 intersect with die faces 65 and 64, respectively, at acute angles.

The die 67 is provided with a heating element 53 by means of which the die faces 51 and 64 can be raised to the fusion temperature of the foam material in sheets 40 and 48. Directly above die face 51 and in registry therewith are the substantially identical, downwardly disposed horizontal die faces 50 and 64 of upper sealing die 66, as shown in FIGURE 7. Die 66 is provided with a heating element 52, similar to heating elements 53 and, like die face 64, die face 65 is relieved by a like amount, providing a total relief of about 0.020" and to about 0.030.

Unlike lower die 67, upper die 66 reciprocates vertically. By means of any suitable reciprocating motor means 57, the upper die 66 is pressed firmly into contact with the strip 40 each time it comes to rest and is retracted before the material begins to move again. Thus, during those periods when the strips 40 and 48 are stationary, they are compressed for a time between the dies 66 and 67.

A shearing type cutter 56 is associated with the upper die 66. The cutter is fitted closely about the entire periphery of die 66. Because the dies 66 and 67 have vertical walls and meet in substantially perfect registry, the cutter 56 can separate material clenched in the die from that lying outside of it. In order to more fully disclose how the cutting and sealing operation may be carried out, reference is now made to an enlarged view, FIGURE 8, showing additional details of the dies schematically represented in FIGURE 5.

As shown in FIGURE 8, the cutter 56 is generally in the shape of an inverted box which partially encloses upper die 66. The cutter includes a base portion 70, attached to motor means 57 in the manner disclosed in FIGURE 5, side walls 69 dependent from base 70 and a hardened cutting insert 68 secured in the lower edge of side walls 69. The insert 68 conforms to the exterior surface of the side walls 75 and 76 of the upper and lower dies 66 and 67 and rings the upper die. The upper die is suspended within the cutter assembly with the aid of bolts 71 which pass through holes 72 in cutter base 70 and threadably engage the upper die backing member 73. The bolts 71 have heads 74 which hang on the upper surface of the backing member. Springs 55 are wound about the bolts between base 70 and upper die backing member. The function of these springs will become apparent as the description unfolds.

The normal condition of the dies, that is their COIldl tion while the sheets 40 and 48 are advancing, is open. The dies normally have sufficient clearance between them to permit the full thickness of both strips 40 and 48 to advance between them without catching. The stroke of the press actually exceeds the aforementioned clearance to the extent necessary to drive the cutter insert 68 at least partly below the surface of lower die face 51. However, since the springs 55 are interposed between the cutter case and the upper die, and because the cutter insert normally rides above upper die face 50, upper die 66 must come to rest and the springs 55 must be compressed to a significant extent before the cutter insert 68 drops below lower die face 51.

When the strips 40 and 48 come to rest, the upper die closes down onto the lower die. The size and strength of the springs 55 is sulficiently great to insure that as the press closes, those portions of strips 40 and 48 which are between die faces 50 and 51 will be substantially completely crushed therebetween before the springs 55 yield to any significant extent under pressure from the motor 57. Thus effective operation of the cutter is prevented until the strips are thoroughly immobilized by being clenched between the die faces. FIGURE 8 illustrates that point in the operation of the cutter-die assembly when the foam material has collapsed but just before the springs yield. Finally the cutter does function severing the material within the dies 66 and 67, while still clenched therein, from the surrounding portions of the strips.

Not only does cutting occur while the press is closed, but the sealing operation also takes place then. Sealing takes place in that narrow region of both sheets 40 and 48 which is held between the die faces 50 and 51. The width of these faces and of die faces 64 and 65 is exaggerated slightly in FIGURES 6, 7, 8 and 9 and even more so in FIGURE 5 to facilitate their illustration. In the region of the strips between die faces 64 and 65, substantially no sealing of a permanent nature takes place, thus providing a foot-opening. Occasionally, there may be some slight bonding in this second region, but it may readily be broken with the fingers without damaging the material or the seam developed in the first-mentioned region.

It will be appreciated that it is not particularly critical whether the seam becomes completely developed before or after the cutter functions. However, it is necessary that the dies remain closed long enough to insure the formation of a good bond in the seam. This usually takes no more than a fraction of a second.

Once both cutting and sealing have been accomplished, the upper die is again opened by reversal of motor 57. As the dies open, the strips of thermoplastic material again advance, and the completed slippers 63 leave the press and are separated from the remaining portions of strips 40 and 48, which are illustrated in FIGURE 5. These remaining portions constitute the waste products of the present method. When the strips 40 and 48 again come to rest, the above described successive steps of closing the dies, forming a seal, cutting away waste material, opening the dies, further advancing the material and bringing the material to rest are repeated again and again on a continuous basis.

An optional added feature of the cutter-die assembly depicted in FIGURE 9 is a pair of spring-loaded plates 76 and 77, secured inside the dies 66 and 67 respectively with the aid of bolts 78. The bolts 75 threadedly engage the aforesaid plates and pass through holes 79 in the dies 66 and 67 and in their respective backing members 73 and 80. Between each of the dies and the respective plate members are secured coil springs 81, which are wound about the bolts 78 and which are slightly less compressible than the thermoplastic foam material.

When the dies are open, eachof the plate members 76 and 77 protrudes slightly from its die. When the die closes down upon the strips 40 and 48, the spring loaded plates exert pressure on the foam material encircled by the die faces 50, 51, 64 and 65, although not compressing the latter material to the same extent as the material between die faces 50 and 51. As a consequence of their relatively light grip on the material, and their somewhat indirect and loose contact with the heating elements 52 and 53 in die backing members 73 and 80, the plates 76 and 77 do not cause any bonding between the strips of thermoplastic foam material. Consequently, their sole function when the press is closed is to immobilize the material. In returning to their protruding condition when the dies open, the plates 76 and 77 will wrest free the slipper and the waste material in the event that they stick to either of the dies, thus facilitating their removal.

The above preferred embodiment illustrates how the invention may readily be practiced with thermal heat sealing apparatus. Our invention may also be practised with electronic sealing apparatus. These two types of aparatus, although they are both thermal in a sense, are distinguishable with regard to the manner of applying the heat to the work. In thermal sealing apparatus, the heat is transferred solely by direct conduction of heat units from a preheated die directly to the material which the die contacts under pressure. U.S. Patent 2,425,388 is an example of this type.

In the so-called electronic type of apparatus, the heat is developed in the material at least in part by subjecting the material to a high frequency alternating field. An example of this type is found in U.S. Patent 2,796,913. Electronic apparatus customarily includes auxiliary heating means of the thermal type. In such a case, the heat is applied to the material partly by conduction and partly by induction. For example, see U.S. Patent 3,026,233.

During the sealing operation, the foam material is squeezed down to a fraction of its uncompressed thickness in the region where sealing takes place. Any effective means of compressing the material may be used. In the case of thermal sealing equipment, the member that transmits both pressure and heat to the material is ordinarily a metal-faced die corresponding to the shape of the desired seam. In electronic equipment, the members between which the sheets of foam are squeezed often comprise a die which is formed basically of metal, but has a facing of Fiberglas reinforced heat-resistant polymer backed up by a layer of elastorneric material intermediate the metal and the facing.

The severing operation may take place while the work is in the grasp of the compression means or after it is released therefrom, the former mode of operation being preferred. The cutting means employed may be manual or mechanical, the latter being preferred for reasons of uniformity of operation, speed and economy. Among the available alternative mechanical means are shearing means such as the one illustrated above, shearing dies, cutting dies and cutting wires. Some of these alternative cutting means are illustrated in U.S. Patents 3,015,601, 3,025,206, and 2,425,388.

From the above description of our methods, it is clear that they are sufficiently versatile to be practised in a variety of types of equipment, only a few preferred representatives of which have been mentioned. Those skilled in the are will readily adapt our methods to types of apparatus not discolsed herein without departing from the steps of our methods. These methods have the advantages of producing articles with a minimum of handling of materials during and prior to production. They can be performed at a great rate of speed with a high degree of product uniformity and few rejects. They are readily adaptable to machinery in which ganged dies, sealing mechanisms and severing means are used to turn out a plurality of objects for each cycle of machine operation.

In accordance with the invention, we have provided a second novel slipper which includes a first piece of heatsealable synthetic polymer sheeting, e.g. foam, forming an upper 82. The upper has a front and side outline approximating that of the front portion of the human foot and terminates in a rear edge 91, which is located about /5 to /2 of the way back along the length of the slipper, and may if desired be folded back upon itself to form a decorative and strengthening, over-lap 84. The upper is joined about its front and side edges with a lower 85, which, to the extent that it coincides with the upper, is of similar shape. Rearwardly of the upper, the lower gradually transitions from its substantially planar configuration, where it coincides with the upper, to a configuration at the heel 86 in which the edges of the lower are turned upward to form the side portions 87 and 88 of the heel. These side portions meet along a heat-sealed seam 89. The upper edge,

e.g. 90, of each side portion intersect with the seam 89 at an acute angle oz, as shown in FIGURE 10.

What we desire to protect by U.S. Letters Patent is:

1. In a slipper comprising first and second elongated pieces of elastic, heat-sealable synthetic polymer sheeting material of similar shape and size defining generally upright side portions, said pieces having first and second ends and elongated upper edges and elongated lower edges which are connected with one another, said first ends being connected by a seam along said ends, said second ends being connected by a heel seam along said second ends and said elongated upper edges being connected by a seam extending over about one-fifth to about one-half the length of said pieces from said first ends towards said second ends, the remainder of said elongated upper edges being substantially free of attachment to one another to define a foot opening, said upper edges intersecting with the heel seam, the improvement characterized in that the slipper is of elastic synthetic polymer foam; the heel seam, viewed with the slipper in a flattened condition, isforwardly inclined for gripping the intended wearers heel when the slipper is in wearing position; the slipper is sufficiently short in relation to the size foot for which it is intended for maintaining the slipper in a stretched condition and for subjecting the heel sea-m to tearing forces when the slipper is being worn; and the upper edges of the side portions viewed with the slipper flattened, intersect the forwardly-inclined heel seam at an acute angle at the point of intersection and are upwardly inclined adjacent said point of intersection for providing a zone of decreased tension in the synthetic polymer foam sheeting around the heel seam in the vicinity of its point of intersection with the edges of the foot opening when the slipper is being worn.

2. A slipper according to claim 1 wherein the heat-sealable polymer foam material is polyurethane foam.

3. A slipper according to claim 1 wherein the connection along said second side is a heat seal extending for about A the length of said pieces.

4. A slipper according to claim 1 wherein both edges of said foot-opening intersect said seam at an acute angle at both ends of the foot-opening.

*5. A method of producing footwear comprising bringing first and second strips of heat-sealable elastic foam material into face-to-face relationship, compressing said sheets in a first narrow region partially enclosing an elongated area having elongated sides and ends, said region extending along and defining a second end, a first elongated side, a first end and a portion of a second elongated side extending about /5 to about /2 of the length of said area from said first end toward said second end, compressing said strips in a second narrow region extending along the remainder of said second elongated side, the compression of said material in said second region being about 0.020 inch to about 0.030 inch less than in said first region, said regions intersecting at acute angles, heating said material in said regions to seal the strips together in said first region only and severing the material within said area and said regions from the remainder of said strips.

'6. A slipper comprising a first piece of synthetic polymer sheeting material forming an upper having a front and side outline approximating that of the front portion of a human foot, and terminating in a rear edge, said upper being joined along its front and side edges to a second piece of said material constituting a lower which, to the extent that it coincides with the upper, is of similar shape and of generally planar configuration, said lower gradually transitioning rearwardly of the upper to a configuration at the heel in which the edges of the lower are directed upwardly to form side portions of the heel of said slipper, said side portions joining one another at said heel in a generally upright, forwardly inclined seam.

7. A slipper in accordance with claim 6 in which said seam and the upper edges of said side portions meet at an acute angle.

8. In footwear of polymeric sheeting material characterized in that the footwear has a heel comprising generally upright side portions which meet at and are secured to one another along a generally upright seam extending an appreciable distance along the heel of the footwear and terminating at a point of intersection with the upper edges of said side portions, the improvement wherein said footwear is of stretchy, elastic synthetic polymeric cellular material and said seam is forwardly inclined for gripping the wearers heel, said upper edges and seam are disposed at an acute angle to one another at their point of intersection, and said intersection is adjacent to the wearers heel.

9. A slipper in accordance with claim 8, wherein said seam is a heat-seal.

References Cited UNITED STATES PATENTS Newton 36-8.1 Zeitz 369 Muller 36-4 X Laven 36-10 X Nygard 36-73 X Scholl 36--8.1

U.S. C1.X.R. 

